Si-29 and Al-27 high-resolution NMR characterization of calcium silicate hydrate phases in activated blast-furnace slag pastes

Within the framework of improving mechanical properties of activated blast- furnace slag cements, a set of hardened pastes of 28 days age were analyzed by Si-29 and Al-27 high-resolution nuclear magnetic resonance (NMR) at 9.4 T. Structural and compositional differences among C-S-H phases obtained wi th different activation and curing conditions were characterized by NMR. Ac tivation of the slag was done with compounds of different alkalinity (sodiu m silicate, sodium hydroxide, calcium hydroxide and gypsum), and under stea m and wet curing. Parameters characterizing the extent of the hydration rea ction, the polymerization degree of the aluminum-silicate chains and the Al /Si ratio in C-S-H were obtained from NMR spectra. Si-29-NMR spectra indica ted that connectivites of silicate tetrahedra in all pastes are compatible with the "dreierkette" structural model of C-S-H. A substantial degree of p olymerization of the aluminum-silicate groups in C-S-H was observed in past es resulting from activation with sodium silicate and gypsum/calcium hydrox ide blend. Steam curing and a higher alkali concentration enhanced the inco rporation of Al in C-S-H. Even with low concentration of alkali, through st eam curing it is possible to obtain a degree of incorporation of Al in C-S- H as high as in the case of higher alkali addition. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.